1. Field of the Invention
The present application relates generally to water maintenance systems for a water feature, and more specifically, to an automated water maintenance system.
2. Description of the Related Art
Balancing the water chemistry (e.g., pH levels and sanitizing agent levels) in water features (e.g., spas or swimming pools) can be a challenging and expensive operation. In particular, “balancing the water” in a spa can be much more challenging than in a pool due to the relatively small volume of water in spas. The number of people per unit volume of water is typically much higher in a spa than in a pool. For example, four people in a 300-gallon spa are comparable to 150 people in an average swimming pool. Because the water chemistry is affected by the frequency of use and the number of bathers, maintaining the water chemistry in spas can require more diligence to maintain than in pools.
Because of the relatively small volume of water in spas, users have significant difficulty in adjusting the pH level using highly concentrated pH-modifying materials, such as acidic materials (e.g., sodium bisulfate) or alkaline materials (e.g., sodium carbonate). In addition, the effects of the acidity or alkalinity of other chemicals, which are added in considerable volumes to sanitize the water, must be addressed in adjusting the pH level. For example, devices such as chlorine or bromine generators tend to increase the pH of the water as a byproduct of the chlorine or bromine generation. Excessive pH levels, either acidic or alkaline, will generally remain in the water until corrected. The persistence of low or high pH levels can cause or contribute to corrosion of metal components of the heater and to scaling of the heater. In addition, because sanitizing agents such as chlorine are less efficient at high pH levels, improper pH levels can lead to unsanitary conditions.
Control of the sanitizing agent (e.g., chlorine or bromine) to ensure that a spa is sanitary is similarly difficult and expensive. Existing systems require operator monitoring and intervention to deal with deviations or low levels of the sanitizing agent. For example, in spas and swimming pools, simple floating dispensers are often used. Such dispensers must be adjusted to a proper feed rate and require attention over a period of days. Variations of the frequency of use of the water feature by bathers or other system parameters can render such devices useless and can require supplemental addition of sanitizing agents to the water. There is a certain forgiveness with the addition of excess sanitizing agent, since excess levels will eventually dissipate or will otherwise be consumed. However, an overfeed condition in which too much sanitizing agent is used can result in corrosion of metal components of the water feature in general, and in the heater in particular.
Manual control of the pH level typically requires the user to test the water at regular intervals using a test kit or test strip and then to “adjust” the pH level by adding several ounces of an acidic material (e.g., sodium bisulfate for spas and muriatic acid for swimming pools). The user must then test again after several hours to ensure that the proper amount of acidic material has been added. If the pH level is still too high, the user must add additional acidic material and wait several hours once again. If the pH level is too low (sometimes the result of today's busy, impatient consumer adding too much acidic material), the user must add a pH-increasing chemical to the water. This repeated addition of chemicals to the water of the water feature in an attempt to control the pH level and the sanitizing agent level is sometimes referred to as “chemical warfare.” Some frustrated consumers often end up draining their spas and starting over with fresh water rather than spending the time and effort to “balance the water.” Other frustrated consumers simply ignore the pH level of the water altogether, which can result in unsanitary conditions due to the reduced efficacy of the sanitizing agent.
Some systems for control of pH levels and/or sanitizing agent levels utilize a peristaltic or diaphragm pump and an open tank. The pump forces a solution into the plumbing of the water feature, usually downstream of the water heater. Peristaltic pumps often require frequent tubing replacements (e.g., every three to six months, depending on usage). Other systems utilize cartridges which are connected via flexible tubing to both the suction and pressure plumbing of the water circulation system. Such systems have the disadvantage of feeding concentrated chlorine at a low pH level directly into the circulation system ahead of the heater, pump, and filter, potentially causing corrosion of these components. Such older systems have largely been replaced by inline feeders which introduce sanitizing agent directly into the plumbing through a pressure differential. These systems can be placed after the heater and other circulation system components.
Other systems for control of sanitizing agent levels utilize a venturi feed and an open tank. The venturi feed creates a vacuum which draws solution into a tee where the solution is mixed with the water being circulated. The feed can be controlled through the use of valves or by manually adjusting a valve on the vacuum side of the tee. Such systems are prone to clogging of the injector orifices.
Erosion feeders are most commonly used on residential and small commercial pools for control of sanitizing agent levels. For example, a feeder containing chlorine tablets can be installed in the return-line plumbing. The tablets are exposed to the flowing stream, and gradually dissolve. Such systems are typically manually adjusted.
Liquid feeders are most commonly used on residential pools. In certain such system, an open tank feeder containing liquid chlorine is connected to the suction and pressure sides of the circulation system. Air is allowed into the feeder to replace the solution as the contents are depleted. A float valve in the feeder maintains the water level in the feeder. Such systems can not be installed below the water level of the water feature due to backflow. Concentrated chlorine enters the water pump and water heater in this arrangement and can damage various equipment of the water feature. Additionally, failure of the float system can cause loss of pool water.
Automatic control of the pH level of a water feature is further complicated by periodic recalibration of the pH controller. Typical pH electrodes have a reference potential defined by a reference gel or solution. This reference material is depleted through migration through the porous junction, resulting in changes of the reference potential. Typically, to calibrate an automatic pH control system, a user must prepare a standard buffer solution (e.g., a pH 7.0 buffer) as a standardizing calibrant, and put the pH controller in calibration mode. The user removes the pH sensor, places it in the container of buffer solution, and recalibrates the pH controller. This procedure can be quite difficult for a user. In addition, the location of the pH sensor can make it difficult to access. The recalibration process is typically performed monthly, or even weekly in some cases, and can require more effort than simply testing and adding chemicals.